1. Field of the Invention
The present invention relates to a printing apparatus, printing apparatus control method, printhead control circuit, and printhead driving method.
More specifically, a printhead comprises a common ink chamber to supply a liquid, a first nozzle array which is arranged in the longitudinal direction of the common ink chamber, and a second nozzle array which is arranged in parallel to the first nozzle array and has a nozzle diameter smaller than that of the first nozzle array. The printhead further comprises a plurality of liquid chambers having openings to first and second nozzles and communicating with the common liquid chamber. A printing apparatus with a printhead drives and controls the printhead that prints on a printing medium by discharging liquids from the first and second nozzles.
2. Description of the Related Art
Along with the recent developments in personal computers, printer technology is also progressing remarkably. A printing apparatus is configured to print an image on a printing paper sheet on the basis of image information.
A printing scheme of a printing apparatus that has recently received a great deal of attention is an inkjet printing scheme. An inkjet printing apparatus discharges ink from a printhead to a printing paper sheet. This scheme allows high-speed printing of high-resolution images and is superior to other printing schemes in various points including running cost and quietness.
The inkjet printing scheme is known to use an electrothermal transducer that generates thermal energy serving as ink droplet discharge energy. In this method, minute nozzles arranged on an inkjet printhead discharge minute ink droplets to print on a printing medium such as a paper sheet.
An inkjet printhead using electrothermal transducers includes a driving system to form ink droplets and a supply system to supply ink to the driving system. The electrothermal transducers are generally provided in a compression chamber. An electrical pulse serving as a print signal is applied to the electrothermal transducers to give thermal energy to the ink. An abrupt phase change of the ink, i.e., the pressure of bubbles generated upon vaporization, is used to discharge the ink.
An inkjet printhead (to be referred to as a printhead hereinafter) normally employs time-divisional drive to execute discharge from the nozzles. Time-divisional drive can improve the ink supply speed and stability and reduce power consumption during discharge. Generally, a plurality of nozzles arranged in a line are divided into several nozzle groups and driven at different timings in each nozzle group.
For example, Japanese Patent Laid-Open No. 2000-071433 proposes time-divisional drive (driving). Nozzles are driven by time-divisional drive at, e.g., a timing shown in FIG. 2. In this example, one nozzle array (one nozzle array will be referred to as one column hereinafter) is divided into groups of 16 adjacent nozzles. The 16 consecutive nozzles are driven at 16 different timings.
In other words, every 16 nozzles are driven at the same timing. Each group of these 16 nozzles is called a block. A method of sequentially driving a plurality of nozzles in each block is called time-divisional drive. Referring to FIG. 2, a indicates breaks in a nozzle array, and b indicates the discharge timings of 16 consecutive nozzles.
The ordinate represents the nozzle position in one column, and the abscissa represents the time. Nozzles 1 to 16 are driven in order. The printhead continuously moves during printing. As a result, dots printed by nozzles 1 to 16 are arranged spatially as indicated by b. Simultaneous with the driving of nozzle 1, every 16 nozzles, i.e., nozzles 17, 34, 49, . . . of the same block are also driven.
To aid in understanding time-divisional drive, nozzles 1 to 16 are sequentially driven in the above description. In actual time-divisional drive, nozzles are distributedly driven on the basis a predetermined driving sequence table. This suppresses the influence of adjacent nozzles in nozzles 1 to 16 when using time-divisional drive.
The mainstream aiming at reproducing a higher image quality is a printhead that has color (magenta, yellow, and magenta) heads each including a large nozzle array (hereinafter also referred to as L nozzle array in the Drawings) and a small nozzle array (hereinafter also referred to as S nozzle array in the Drawings), as shown in FIG. 3. This printhead can produce a high-quality image by combining large ink droplets discharged from the large nozzle arrays and small ink droplets discharged from the small nozzle arrays.
An inkjet printer disclosed in, e.g., Japanese Patent Laid-Open No. 08-183179 prints by using an inkjet printhead that has orifices capable of discharging ink droplets of a plurality of sizes while sequentially changing the ink droplet size during single scanning or in every scanning.
The inkjet printer of Japanese Patent Laid-Open No. 08-183179 proposes shifting the ink droplet discharge timing. Namely, this prior art proposes shifting large ink droplets discharged from large nozzles (hereinafter also referred to as L nozzle in the Drawings) and small ink droplets discharged from small nozzles (hereinafter also referred to as S nozzle in the Drawings) relative to a printing paper sheet so that the ink droplets of the plurality of sizes can compensate for each other.
As inkjet printers are recently becoming cheaper, the cost of printheads also must be reduced. A low-cost printer uses a printhead that uses common driving and heat pulse signals for the large and small nozzle arrays of color heads so as to simplify logic and driving circuits including the shift register in the printhead.
More specifically, a specific bit, i.e., bit16 (SEL) in printhead driving data shown in FIG. 4 selects the large nozzle arrays or small nozzle arrays by bit logic. The large nozzle arrays or small nozzle arrays are selectively driven on the basis of the state of the bit.
Since the heat pulse signal is common to the large nozzle arrays and small nozzle arrays, it is impossible to select a small nozzle array for one color and a large nozzle array for another color. This is because the heat pulse time is different for the large nozzle array and the small nozzle array. If a heat pulse suitable for a large nozzle array is applied to a small nozzle array, an ink discharge heater corresponding to the small nozzle array may break.
For this reason, a color head that has common driving and heat pulse signals for the large and small nozzle arrays must sequentially toggle-drive the large nozzle array and small nozzle array alternatively so that they can discharge ink during single scanning.
Conventional toggle printing by large nozzle arrays and small nozzle arrays is done for each column, i.e., each nozzle array. FIG. 5 is a view schematically showing a state wherein dots are printed by first driving the nozzles of a large nozzle array and then those of a small nozzle array. Referring to FIG. 5, in driving the nozzles of the large nozzle array, nozzles L0 to L15 are driven in order. Even in driving the nozzles of the small nozzle array, nozzles S0 to S15 are driven in order. The relationship between nozzles and blocks will be described. The nozzle L0 is a nozzle of a block (large block 0) of the large nozzle array. The nozzle L1 is a nozzle of another block (large block 1) of the large nozzle array. The nozzle L15 is a nozzle of still another block (large block 15) of the large nozzle array. The nozzles and blocks of the small nozzle array have the same relationship as in the large nozzle array. In FIG. 5, it looks as if blocks 0 to 15 are driven in order. However, in actual driving, a driving sequence table designates block driving distribution to prevent continuous operation of adjacent blocks.
As shown in FIG. 5, blocks 0 to 15 included in one column within 1,200 dpi drive all nozzles within the driving resolution of the large nozzle array or the small nozzle array. The method of selectively driving each of the large nozzle array and small nozzle array is called “column toggle printing”.
Since this method switches print data for each column, the large nozzle array and small nozzle array can share a buffer (to be described later) to latch nozzle data. A large circuit scale is not necessary for column toggle printing.
The number of nozzles of a color head is steadily growing because the market requires a higher print speed even in a high-quality print mode. When the large nozzle array and the small nozzle array are switched for each column, the difference in the amount of ink discharge between the large nozzle array side and the small nozzle array side increases as the number of nozzles increases. FIG. 6 shows the schematic structure of nozzles included in a large nozzle array and a small nozzle array. FIG. 7 is a sectional view taken along a line X.
Referring to FIG. 6, a plurality of nozzles 1 discharge ink. A plurality of ink chambers 2 have openings to the nozzles 1. A long common ink chamber 3 supplies ink to the ink chambers 2. The nozzles are divided into a large nozzle array and a small nozzle array which are arranged on both sides of the common ink chamber 3. In column toggle printing that selectively drives the large nozzle array and the small nozzle array for each column, the amount of the ink discharge on the large nozzle array side and on the small nozzle array side are different. This creates ink imbalances in the common ink chamber 3, and consequently increasin the possibility of hindering ink refill in the ink chambers 2 and causing discharge errors.